The invention relates to an apparatus for staining sample sections, in particular ultrathin sections, having a chamber, in which sample sections can be fastened, and having a pump for pumping liquids through the chamber, the chamber having an inlet and an outlet, the inlet being able to be connected to at least one reservoir of a staining liquid via inlet lines which can be controlled by valves.
Staining apparatuses of this type are well known. The thin sections which are to be treated in the staining apparatus are prepared in particular for examination in an electron microscope. A number of sample sections, e.g. up to 25, are processed in an air-tight sealed chamber with a programmable sequence of staining solutions which are channelled through the chamber, to be precise. The staining liquids are—usually interspersed by rinsing steps using water—pumped into the chamber in which the thin sections are located and held by so-called grids as carriers.
A staining method of particular importance is so-called double staining. The staining solutions used in this case are uranyl acetate and lead citrate solutions, which are problematic on account of their susceptibility to vibrations and contact with unwanted surrounding substances, but also due to their toxicity. Lead citrate in particular forms insoluble precipitates with carbon dioxide particularly easily, which are deposited on the sections and/or in the lines. If washing programs are not carried out reliably, this results in failure of the apparatus (contamination of the hoses, valves and the pump).
A program sequence of double staining for example comprises the following steps: filling the chamber with water, replacing the water with the first staining liquid (“Stain 1”=uranyl acetate solution), replacing the liquid with water for rinsing, replacing the water with the second staining liquid (“Stain 2”=lead citrate solution), replacing the liquid with water. However, individual program steps can be changed.
Manual staining is an alternative to automated staining. In this case, a number of drops of the required liquids are applied next to each other on a clean base (e.g. Parafilm), namely in each case the uranyl acetate solution, water, the lead citrate solution and water again. Each grid (with the section on the underside) is applied in succession onto the drops with the aid of tweezers. Although this method uses small quantities of the staining liquids, it is very error prone—in particular if a large number of sections are to be treated—and the user easily comes into contact with the toxic solution substances.
A staining apparatus for the automated implementation of double staining of thin sections is the applicant's “μM STAIN” apparatus. In the case of this apparatus, conventional magnetic valves with Teflon seats are used to control the liquid supply. The liquids are pumped through Teflon hoses, which are distinguished by a high resistance but are rather brittle, by means of a ceramic or a membrane pump. The treatment of the sensitive staining liquids is still problematic in the case of this apparatus. That is to say, it has been shown that the line-pump systems are particularly sensitive to precipitates, which can lead to blockages of the pump, malfunctions of the valves or obstructions in the hose lines. Furthermore, the ceramic pumps in particular have been found to be susceptible to the transported chemical substances. The valves and the pump itself usually cannot be cleaned sufficiently in the case of servicing and thus have to be replaced by new ones, which leads to very high service costs.